Technical Field
The present invention relates to a piezoelectric device such as an acoustic element, piezoelectric actuator, etc., particularly suitable for use in a high-temperature environment, as well as a piezoelectric ceramic composition used for such piezoelectric device.
Background Art
Piezoelectric ceramic compositions are used as electromechanical conversion materials for piezoelectric devices such as acoustic elements, piezoelectric actuators, etc.
For example, Patent Literature 1 discloses a ferroelectric ceramic constituted by a perovskite solid solution expressed by Pb1-(3/2)aMa{(Ni1/3Nb2/3)1-b(Zn1/3Nb2/3)b}xTiyZrzO3 [where M is at least one type of element selected from a group that includes La and Nd, and x+y+z=1, a=0.005 to 0.03, b=0.5 to 0.95, x=0.1 to 0.4, y=0.3 to 0.5 and z=0.2 to 0.5] and containing 0.3 to 1.0 percent by weight of MnO2.
Piezoelectric devices are adopting laminated structures in recent years for the purpose of performance improvement, lowering of driving voltage, and so on.
However, the ferroelectric ceramic in Patent Literature 1 involves a high sintering temperature of 1130 to 1300° C. and therefore requires a lot of thermal energy for sintering. In addition, an Ag alloy with high Pt or Pd content must be used as the material for internal electrodes to be sintered simultaneously with the ferroelectric ceramic, which presents a problem of adding to the cost of the piezoelectric device.
In light of the above, piezoelectric ceramic compositions that can be sintered at low temperature have been developed to lower the costs of piezoelectric devices.
Patent Literature 2 discloses a piezoelectric ceramic composition constituted by a perovskite composition expressed by Pba{Zrb.Tic.(Ni1/3Nb2/3)d.(Zn1/3Nb2/3)e}O3 [where b+c+d+e=1, 1.000≦a≦1.020, 0.26≦b≦0.31, 0.34≦c≦0.40, 0.10≦d≦0.35 and 0.07≦e≦0.14] and also by Ag2O contained in the perovskite composition, wherein this Ag2O is contained by a ratio of 0.005 to 0.03 percent by weight, and it is claimed that this piezoelectric ceramic composition can be sintered at 900° C. or so.